1. Field of the Invention
The present invention relates to a flat display device, and more particularly, to a flat display device with a larger display area and greater resistance to deterioration by moisture.
2. Discussion of the Background
Flat display devices, such as liquid crystal displays (LCDs) and organic or inorganic electro-luminescent (EL) displays, may be categorized as passive matrix (PM) or active matrix (AM) type depending on how they are driven. In a PM display, a plurality of anodes and cathodes may be arranged in columns and rows, respectively, and a row driving circuit transmits a scan signal to a cathode selected from a row. Also, a column driving circuit may input a data signal into each anode.
An AM display is widely used for displaying moving pictures since it processes a great number of signals by using a thin film transistor (TFT) to control the signal input to each pixel.
An organic EL display has an organic luminescent film between an anode and a cathode. Applying an anode voltage and a cathode voltage to the anode and the cathode, respectively, transports holes, introduced from the anode, to the luminescent film via a hole transport layer (HTL), and electrons, introduced from the cathode, to the luminescent film via an electron transport layer (ETL). The electrons and the holes combine in the luminescent film to produce excitons. As the excitons change from an excited to ground state, fluorescent molecules on the luminescent film emit light to form an image. Red (R), green (G), and blue (B) pixels may be utilized in a full-color organic EL display.
However, in the organic EL displays, organic films are susceptible to moisture. Thus, various techniques of sealing the display region with a substrate or metal cap have been proposed to protect the organic luminescent film from moisture and to protect the display region from physical shock.
FIG. 1A is a plan view of a conventional AM type organic EL display, and FIG. 1B is a cross-sectional view taken along line I-I of FIG. 1A.
Referring to FIG. 1A and FIG. 1B, the AM type organic EL display includes a display region 20 located on a transparent insulating substrate 10. The display region 20, which includes an organic light emitting device (OLED), is hermetically sealed by bonding a metal cap 90 to the transparent insulating substrate 10 using a sealant 81. The OLED includes a TFT and a plurality of pixels. A cathode 40, which is one electrode of the OLED, is located on the display region 20 and connected to an external terminal region 70 via an electrode power supply line 41. A plurality of driving lines 31 is installed in the display region 20 and connected to the terminal region 70 via a driving power supply line 30, which is located outside the display region 20. A vertical circuit portion 50 and a horizontal circuit portion 60 are located outside the display region 20 and connected to the terminal region 70 via circuit lines 51 and 61, respectively. The vertical and horizontal circuit portions 50 and 60 transmit signals to the TFT of the display region 20.
In this AM type organic EL display, the metal cap 90 covers the display region 20, the circuit lines 51 and 61, and the vertical and horizontal circuit portions 50 and 60. In other words, the metal cap 90 covers the entire region except the terminal region 70. Accordingly, the sealed portion includes not only the display region 20, but also the circuit lines 51 and 61 and the s circuit portions 50 and 60, which do not actually display images. This structure decreases the size of the display region 20 relative to the entire display device, thereby providing a larger non-radiative region, or dead space.
For this reason, with the organic EL display shown in FIG. 1A and FIG. 1B, the circuit lines 51 and 61 that connect the display region 20 and the terminal region 70 must be thinned, increasing their resistance.
Hence, for the reasons noted above, an organic EL device having a larger display region that is adequately protected from moisture is desired.